The proton exchange membrane fuel cell (PEMFC) is the first fuel cell that is put into practical use. It is also a fuel cell receiving increasing attention nowadays. That is due to the fact that the specific power and power density of PEMFC are higher than those of the other types of the fuel cells. In addition, since the operating temperature is low, PEMFC are suitable to be used as electric source for vehicles, as small stationary electric source and as portable electric source.
Compared with PEMFC, methanol is used in place of hydrogen as the fuel in a direct methanol fuel cell (DMFC). Except those that PEMFC possess, DMFC owns some other advantages. Therefore DMFC has the advantages that PEMFC has. Because methanol is abundant in resource, cheap in price and is a liquid convenient to be stored and carried, DMFC is more suitable to be used as a portable electric source in military and civil fields. Since the nineties of 20th century, more and more attention has been gradually drawn to DMFC.
After nearly forty years of research on PEMFC, great breakthrough was made in the basic research as well as in the engineering fields. However, from the cost-effectiveness viewpoint, the properties of PEMFC are far below the commercial demands. One reason is the high price of the electrode catalyst and electrolyte membrane. At present, platinum and its alloy are mostly used in anode catalyst while platinum is used in cathode catalyst. Researches have shown that certain non-platinum catalyst can be used to replace cathode Pt/C catalyst whereas platinum must be used in an anode catalyst. On the other hand, there exists a so-called “methanol crossover” problem in DMFC. That is, methanol would permeate through the electrolyte membrane and enter the cathode, producing mixed potential and causing the lowering of the cell efficiency and the methanol utility. In order to lower the cost of PEMFC and DMFC, to reduce the consumption of the limited platinum resource on the earth and to eliminate the influence of “methanol permeation” on the performance of the cell, it is necessary and urgent to develop a non-platinum and methanol-resistant electrocatalyst for the cathode of a fuel cell. For the moment, the transition metal macrocyclic compound is one of the mostly studied methanol-resistant and non-platinum cathode electrocatalysts, especially the porphyrin or phthalocyanine compounds having Fe or Co as the central metal. The porphyrin or phthalocyanine compounds possess high catalytic activity for oxygen reduction as well as good resistance to methanol [S. Gupta, D. Tryk, S. K. Zecevic, W. Aldred, D. Guo, R. F. Savinell, J. Appl. Electrochem., 28, (1998) 673–682]. However, the stability of the catalysts is low, because hydrogen peroxide produced in the course of the oxygen reduction will corrode the active carbon carrier and transition metal macrocyclic compounds and deteriorate the performance, which affects their practical use adversely.